Allah states here that the worst moving creatures on the face of the earth are those who disbelieve, who do not embrace the faith, and break promises whenever they make a covenant, even when they vow to keep them,

وَهُمْ لاَ يَتَّقُونَ

(and they do not have Taqwa) meaning they do not fear Allah regarding any of the sins they commit.

فَإِمَّا تَثْقَفَنَّهُمْ فِى الْحَرْبِ

(So if you gain the mastery over them in war), if you defeat them and have victory over them in war,

فَشَرِّدْ بِهِم مَّنْ خَلْفَهُمْ

(then disperse those who are behind them,) by severely punishing the captured people according to Ibn `Abbas, Al-Hasan Al-Basri, Ad-Dahhak, As-Suddi, `Ata' Al-Khurasani and Ibn `Uyaynah. This Ayah commands punishing them harshly and inflicting casualties on them. This way, other enemies, Arabs and non-Arabs, will be afraid and take a lesson from their end,

لَعَلَّهُمْ يَذَّكَّرُونَ

(so that they may learn a lesson. )

As-Suddi commented, "They might be careful not to break treaties, so that they do not meet the same end."